gtk_combo_box_entries and empty text

gtk_combo_box_entries and empty text

Passing -1 to gtk_combo_box_set_active, seems not to work as the gtk
documentation explains; there might be a bug in the library or some
special case that is not explained.

could be related to:
  http://mail.gnome.org/archives/gtk-devel-list/2004-March/msg00170.html

passing \n seems to "trick" the cell renderer to clear the entry
completely.  This is a temporary solution.

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>